In absolute dating what radioisotope is used
Many rocks and organisms contain radioactive isotopes, such as U-235 and C-14.
These radioactive isotopes are unstable, decaying over time at a predictable rate.
The same rock formation also contains a type of trilobite that was known to live 415 to 425 million years ago.
Since the rock formation contains both types of fossils the ago of the rock formation must be in the overlapping date range of 415 to 420 million years.
It can only be used to date fossils younger than about 75,000 years.Potassium-40 on the other hand has a half like of 1.25 billion years and is common in rocks and minerals.This makes it ideal for dating much older rocks and fossils.C and counting the amount of each) allows one to date the death of the once-living things.Perhaps you have heard of Ice Man, a man living in the Alps who died and was entombed in glacial ice until recently when the ice moved and melted.